mb/google/brya/var/agah: Disable ASPM for dGPU

Since ASPM is not verified as fully functional yet, and the board is
still in development, this patch disables ASPM for the dGPU.

BUG=b:236676400
TEST=boot to OS in agah, lspci -vvv shows ASPM is disabled

Signed-off-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Change-Id: I525eeb18c57d45fd55335b63a59262066afc9567
Reviewed-on: https://review.coreboot.org/c/coreboot/+/65566
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Ivy Jian <ivy.jian@quanta.corp-partner.google.com>

src/mainboard/google/brya/variants/agah/overridetree.cb

@@ -71,6 +71,7 @@ chip soc/intel/alderlake
 				.clk_req = 0,
 				.clk_src = 0,
 				.flags = PCIE_RP_LTR | PCIE_RP_AER,
+				.pcie_rp_aspm = ASPM_DISABLE
 			}"
 			device pci 00.0 alias dgpu on end
 		end

src/mainboard/google/brya/variants/agah/variant.c

@@ -132,6 +132,10 @@ static void dgpu_power_sequence_on(void)
 
 void variant_init(void)
 {
+	/* Disable ASPM for the GPU until it is verified working. */
+	struct device *dgpu = DEV_PTR(dgpu);
+	dgpu->disable_pcie_aspm = 1;
+
 	if (acpi_is_wakeup_s3())
 		return;